What is RAID?
RAID Stands for Redundant Array of Independent Disks.It is a set of technology used for teaming disk drives to improve performance and fault tolerance of the servers .It is a way of storing the same data in several different places (thus redundantly) on multiple hard disks.By placing a data on several disks I/O (input/output) operations can be continued in a balanced way. As multiple disks increases the mean time between failures, storing data redundantly also increases fault tolerance.It is a technolgy developed in which a huge number of low cost hard drives could be linked with each other to form a single large capacity storage device which provide outstanding performance, storage capacity and trustworthy over older storage solutions. It is a deployed method which is used widely for storage in the enterprise and server markets.
There are different types of RAID from which some are as follows:-
RAID-0 : Striping
RAID-1 : Mirroring and Duplexing
RAID-2 : Error-Correcting Coding
RAID-3 : Bit-Interleaved Parity
RAID-4 : Independent Access with Dedicated Parity Disk
RAID-5 : Independent Access with Distributed Parity
RAID-0 : It uses striping to write data on multiple drives simultaneously. This means that when you write a 4GB file across 4 drives, 1GB of data is written to each drive. Parallel reading of data from multiple drives can have a remarkable positive impact on performance and reliability.Double the amount of data can be written in a given time frameon to the two different drives compared to that same data being written to a single drive.
Note:RAID-0 improves the performance of the server but does not deliver a fault tolerance.This means If one drive fails then all data in the array is lost.
RAID-1 : RAID 1 uses mirroring technology to write data on multiple drives. When you write a file, the file is actually written on to two different disks at the same time. If one of the disks fails, you simply replace it and rebuild the mirror.With RAID 1 you must purchase double the amount of storage space that your data requires.
RAID-2 : RAID 2 uses for error correction codes it is meant to use with drives which do not have built-in error detection. All SCSI drives support built-in error detection, so this level is of little use when using SCSI drives.
RAID-3 : It stripes data at a byte level across several drives, with parity stored on single drive. It is otherwise similar to level 4. Byte-level striping requires hardware support for efficient use.
RAID-4 : RAID 4 stripes data at a block level across several drives, with parity stored on single drive. The parity information allows you to recover from the failure of any single drive. The performance RAID 4 is very good for reads . Writes, however, require that parity data be updated every time. This slows small random writes, in particular, though large writes or sequential writes are fairly fast. Because only one drive in the array stores redundant data, the cost of per megabyte of a RAID 4 can be fairly low as compare to others.
RAID-5 : It provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID .This slightly reduces available disk capacity, but it also means that the RAID array continues to function if a single disk fails. In the event of a disk failure, you simply replace the failed disk and keep working.